If you have mailed your offer letter by Certified Mail with a Return Receipt Requested through the post office, you will be able to know when the creditor has picked up the letter. If you did not send your letter with tracking, there is no way to track if the letter was received.
When sent by Certified Mail with Return Receipt Requested, once the creditor has signed for your letter at the post office, you will receive a notice in your mail. This will be a green card showing you the date and representative’s name and signature that signed for the letter. If you opted to be notified by email, you will also receive an email notification showing the same information.
Keep in mind that just because the creditor has picked up your letter, it doesn’t necessary mean that you will receive a response from them soon, or at all. Some creditors are quick to respond to offer letters, while others take their time. And some creditors may never respond to your offer. For more information about this, you can read more here: 'How long does it take to receive a response from the creditor to my offer?'